| 摘要 |
A level including an elongate hollow frame with two sidewalls and a topwall 130 and a bottom wall extending between. A central vial (50, fig 8) is within a topnotch formed by removal of a topwall section and adjacent sections of sidewalls including notch-defining bottom and side edges. The frame includes an inner horizontal wall 30 extending between the sidewalls at the notch-defining bottom edges (21, fig 5), reinforcing the frame weakened by material removal for the topnotch. The central vial may be supported in accurate orientation without calibration against a central-vial reference surface formed in the inner horizontal wall 30 parallel to the top and bottom measuring surfaces and defining a notch-bottom. An integral inner vertical wall 35 may extend between the top and bottom walls thereby reinforcing the frame along the frame length. A plumb-vial structure may be present and may have a viewing-end region which includes an elongate ramp sloping along a level-longitudinal axis toward the plumb vial with an inclination permitting vial viewing from shallow angles. The level may preferably include an external brace reinforcing a central frame portion weakened by forming the topnotch. |
